8.3 Coral reefs Flashcards
What is the importance of coral reefs?
- Seafood: yield up to 15 tons of fish/other seafood per km squared
- estimated can provide food for up to a billion people in Asia alone
- Tourism: snorkelling/scuba diving is especially popular in the Red Sea
- much needed income in LICs
- Medical products: in rainforest some of the organisms living in the reef produce chemicals that can be used to cure disease, potentially including skin cancer and some viral diseases
- Coastal protection: coral reefs protect coastline from storm waves and can even break the power of tsunami waves
- especially important in areas where storms likely
- jewellery
What are the different types of coral reefs?
fringing reefs: grow near coastline around island/continents. Most common type.
barrier reefs: parallel to coastline, but separated by deep wide lagoons. At their shallowest points, they can reach water’s surface forming a “barrier” to navigation
atolls: rings of coral that create protected lagoons and are usually located in middle of the sea. Usually form when islands surrounded by fringing reefs sink into the sea/sea levels rises around them.
What are the conditions needed for coral growth?
Light:
- most cannot grow in the water deeper than 35m as need sunlight to photosynthesise
- corals feed on xoolanthae, need sunlight
Wave action:
- sufficient wave action which oxygenates the water so that the coral polyps can respire
- but too strong wave action can damage the structure of the calcium carbonate skeletons and risk erosion occurring increasing sediment levels
Salinity:
- grow best where salt levels are high
- prefer seawater with salinity levels between 32 and 42 psu
Sea bed:
- has to be solid surface which reef can grow on
- so form in shallow offshore waters
Sediment:
- polyps need Clean, clear, sunlit water so can’t live where rivers bring muddy sediments into sea and also need sediment clogs up feeding systems of coral polyps
Exposure to air:
- can’t survive for long above the water, so most of the reef is at or below low tide level
Temperature:
- must be above 18 degrees
- grow best where sea surface temp between 23 and 25 degrees why most are found between 30 degrees north and south of the equator
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What is the characteristics of an Atoll?
- Shape: ring-shaped coral reef enclosing a lagoon
- Lagoon: central lagoon, often relatively shallow
- Biodiversity: high biodiversity, with a variety of coral species, fish and other marine life
How do Atolls form?
- darwinian theory of formation: links three types of reef into progression
- atolls consist of a ring shaped piece of coral situated away from the shore with a deep central lagoon
1. Volcanic island forms and a reef starts to grow around the island parallel to the coastline, forming a fringing reef
2. Island then begins to subside; it sinks due to rising sea levels or plate tectonics
3. This forms a central lagoon up to 50 meters deep and the reef separates fro the island forming a barrier reef
4. Complete submergence of the island then occurs but the coral reef continues to grow upwards as it has increased input available and the central lagoon becomes deeper - atoll
What is the distribution of atolls?
Geographic distribution: found in pacific/indian oceans
Pacific ocean: e.g Caroline, Marshall and Tuamotu archipelagos
Indian Ocean: Maldives
What are the characteristics of Fringing Reefs?
Proximity to shore: directly attached to the shore with no significant lagoon between reef/land
- Slope: gentle slope on shoreward side and steeper slope on seaward side
- Biodiversity: diverse
- Water depth: shallow water
How do fringing reefs form?
- Coral polyp settlement: coral larvae settle on submerged rocks/hard surfaces in shallow waters
- Growth and colonisation: these larvae develop into coral polyps, which beging to grow to form colonies. As they thrive, they secrete calcium carbonate, creating hard skeleton that contributes to the reef strucutr
- Expansion: as more polyps settle and grow, reef expands outward from the shore
What is the distribution of fringing reefs?
- Tropics: found where water temps suitable
- Caribbean: Bahamas
- Red sea: coastlines of Egypt
- Pacific oceans: coastline of Australia
What are the characteristics of barrier reefs?
- distance from shore: separated from mainland by wide, deep lagoon
- Lagoon: several km wide and vary in depth
- size: larger/more continuous than fringing reefs, stretching hundreds of km
- biodiversity: high
What is the formation of barrier reefs?
- Initial fringing reef stage: start forming adjacent to the coast
- subsidence and separation: as land/island subsides lagoon forms between the reef and the shore
- reef growth: coral continues to grow upwards/outwards, maintaining its position near the surface as land subsides
What is the distribution of barrier reefs?
- Great barrier Reef: Queensland, Australia
- Belize barrier Reef: coast of Caribbean sea
- New Caledonia Barrier Reef: southwest pacific ocean
How does global warming threat coral reefs and impacts?
Threat:
- coral bleaching occurs when ocean temps too high for algae to survive in corals
- more diseases and invasive species may thrive in warmer waters potentially harming corals
- more frequent, strong storms can disrupt/destroy coral reefs
- higher levels of CO2 lead to acidification, makes it harder for corals to produce their calcium carbonate skeletons
Impacts:
Environmental:
- bleaching kills coral = loss of diversity/habitat
Social:
- loss of jobs due to decrease in tourism
- families may struggle who rely heavily on resources from ocean
- 50% drugs made for humans derived some way from nature
Economic:
- loss of tourist will occur if coral becomes unattractive = loss of GDP for gov who rely on it
How does sea level rise threat coral reefs and what are its impacts?
Threat:
- increase in temperature = glaciers/ice sheets melting = rise in sea level
- if sea levels rise faster than upward growth of coral, may be too deep to receive sufficient sunlight
- rise in sea levels can cause increased coastal erosion, so more sediment is transported to the oceans, can lead to sedimentation in coral reefs, blocking sunlight
- especially in fringing reefs as close to shoreline
How does El Nino threaten coral reefs ?
Threat:
- El Nino is a climate pattern that causes unusual warming of surface waters in the eastern Pacific Ocean
- may raise chances of coral bleaching across Great Barrier Reef
- during 2015-2016 even experienced prolonged periods of elevated sea temps
How does acidification threaten coral reefs?
- significant increase in CO2 levels in the ocean
- when absorbed by seawater, triggers chemical reactions that result in increase in levels of H+ ions and decreases pH (more acidic)
- coral become bleach
- ocean’s pH dropped by about 0.1 units since start of industrial revolution
Impacts:
Environmental: coral cannot maintain calcium carbonate structures needed for growth/survival
- then leads to weaker coral skeletons = increased vulnerability to erosion
Social:
- fish begin to decline, health of relying locals does too
Economic:
- income/employment declines
How is land based pollution a threat to coral reefs?
- chemicals in agricultural fertiliser = increased number of the Crown of Thorns starfish which warm oceans
- areas around ports have large amounts of shipping that also pollutes the sea, especially plastic waste which can smother/kill the coral
- raw sewage from tourism/coastal towns pollute seawater, cause water to be murky and block light affecting photosynthesis of algae
- even treated sewage and issue, contains phosphates from detergents which encourage growth of phytoplankton and crown of thorns starfish
How is physical damage a threat to coral reefs?
- boating can physically disrupt coral reefs, e.g anchor dropped or large boats may bulldoze through and destroy coral
- destructive fishing practices can damage reefs: e.g bottom-trawling where large net dragged on sea floor
How is tourism a threat to coral reefs?
- every year, 70 million trips to visit coral reefs for leisure
- tourism can form foundation for jobs, income and awareness, however tourists can also trample on the coral/disturb ecosystems
Impacts:
Environmental:
- breakage of coral colonies and tissue damage with direct contact such as walking and touching common when snorkelling
- water pollution by tour boats fuel discharge and human waste
- invasive species spread through fouling from recreational boating
Social/economic:
- less fish for locals to eat
- project 70% of reefs to vanish before 2030
What are the main threats to Florida Keys coral reef? (case study)
- Local shops, such as Dive Key West shop, which sells scuba gear and runs boat charters rely on a healthy reef system, divers not interested in exploring dead/damaged reefs which do not attract as many fish and can be covered in algae
- Tourism is the economic engine of the Florida Keys – three and half million people visit each year and tourism supplies 54% of all island jobs and fuels a $2.7 billion economy**
- Less than 10% of the reef system is now covered with living coral
- reefs experienced back-to-back major bleaching events in 2014 and 2015
- Global warming main threat:
- Strong El Nino event of 1997-1998 which triggered widespread bleaching/coral death around the world
- 21 coral species in the Florida Reef Tract are suffering from multiple diseases and 7 of those are threatened under the Endangered Species Act
- Coral reefs worth $36 billion annually to tourism industries in key tropical coastal regions such as Florida/Hawaii
What are the management strategies for florida keys coral reef (case study)?
- 20 feet under water at Pickles Reef, the Coral Restoration Foundation, based in Key Largo has implanted endangered staghorn corals across the reef
- The implants, are small but are growing steadily
- Federal program that certifies vessels that train their crews in proper coral protection practices, including following proper mooring rules/ensuring divers do not poke/prod the reefs
Managing Coral reefs
- protected areas and exclusion zones
- preventing and controlling invasive species/predators: removing crown of thorns starfish
- limiting global warming/ocean acidification: greener energy sources
- education and awareness: sustainable driving practices
great barrier reef importance
Biodiversity:
- 400 types of coral
- 1,500 species of fish, 4,000 species of mollusks
- over 215 bird species
Economic significance:
- tourism: over 2 million visitors annually, generating approximately AUD $6.4 billion and supporting 64,000 jobs
Threats to the Great Barrier Reef
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coral bleaching/climate change:
- mass bleaching in 2016, 2017 and 2022 - affected over 60% of the reef - cyclones: Cyclone Yasi (2011) and Cyclone Debbie (2017), cause significant physical damage to coral structures.
- Agricultural runoff & water pollution: rivers like Burdekin and Fitzroy carry fertilisers from Queensland farms
- Pollution/invasive species:
- Increased outbreaks of crown-of-thorns starfish that feed on coral - surveys recording up to 100 COTS per hectare - commercial fishing: trawling in GBR: one trawl damage 15% of reef and five trawls can lead to loss of 90%
management efforts in great barrier reef
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Great Barrier Reef Marine Park Authority (GBRMPA):
- established 1975: manages and regulates human activities in the reef area.
- Implemented zoning plans -
Reef Water Quality Plan:
- Between 2009 and 2019, reductions in nitrogen runoff (28%) and sediment runoff (11%) were recorded.
- Promotes sustainable farming practices:
- Use of cover crops to prevent soil erosion.
- Reduction of fertilizers and pesticides through precision farming techniques. -
Crown-of-Thorns Starfish (COTS) Management:
- Targeted removal campaigns using divers to manually cull starfish.
- Deployment of robotic systems like the COTSbot, an underwater drone designed to locate and inject lethal doses of bile salts into starfish
- 1.2 million starfish removed since start of program in 2012 -
Zoning Plan (2003):
- Great Barrier Reef Marine Park Zoning Plan divides the reef into different zones with specific restrictions
- 33% of the reef is protected from extractive activities, creating marine sanctuaries where ecosystems can recover
